The radiation monitor has been widely used at the exits and entrances of customs, borders, airports, nuclear power plants and other important places for preventing illegal transport of radioactive materials. A prior art radiation monitor detects the Gamma and neutron rays emitted by the radioactive materials/special nuclear materials when they are passing through the monitor, and determines whether an object under examination contains radioactive materials/special nuclear materials according to the abnormal changes of the count rate or the spectrum of the system caused by the Gamma and neutron rays.
Besides radioactive material monitoring, the incoming or outgoing articles at the entrances and exits of an important place are also performed with X-ray Non Intrusive Inspection (NII). A prior art NII system uses an X-ray machine as a radiation source, detects the dosage of X-rays that penetrate an object under examination when the object passes through, obtains the mass thickness and image information of the object according to the change of detected penetrated dosage, and thereby determines whether a dangerous article is contained.
The above-mentioned radiation monitor and NII system can perform their respective functions in different fields of examination, but a problem exists that they cannot be put adjacent to each other to perform radioactive material monitoring and X-ray detection on the same object. The reason lies in that when performing X-ray radiation imaging examination on an object under examination, the X-ray NII system will emit a lot of X-rays, wherein some of these X-rays will leak to the adjacent radiation monitor. Since the radiation monitor judges whether the passed object under examination contains radioactive materials just by detecting rays, the leaking X-rays from NII system will affect the precision of detection of the radiation monitor and make it unable to correctly judge whether the detected abnormal radiation is caused by any radioactive material or by the NII system. Moreover, since said radiation monitor and the X-ray NII system cannot be put adjacent to each other, goods have to be transported between the radiation monitor and the X-ray NII system at the customs of the airports or the seaports, which results in a great waste of manpower, resources, space and time.